1. Field of the Invention
Generally, the present invention relates to an optical radiation sensor system.
2. Description of the Prior Art
Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems.
It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum “dose” level (often measured in units of microwatt seconds per square centimetre). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UV Max™ and Trojan UV Swift™, employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation. Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the trade-names UV3000™ and UV4000™, employ the same principle to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of a treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:                U.S. Pat. No. 4,482,809,        U.S. Pat. No. 4,872,980,        U.S. Pat. No. 5,006,244,        U.S. Pat. No. 5,418,370,        U.S. Pat. No. 5,471,063,        U.S. Pat. No. 5,504,335,        U.S. Pat. No. 5,539,210, and        U.S. Pat. No. 5,590,390 (Re.36,896).        
In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water under treatment. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection or treatment process. The information so-obtained may be used to control lamp output to a desired level and/or determined when it would be desirable to clean the exterior of the protective sleeves typically used to contain the radiation lamp(s).
It is known in the art to monitor the ultraviolet radiation level by deploying one or more sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These sensor devices may be photodiodes, photoresistors or other devices that respond to the impingement of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (e.g., in volts or amperes) on output leads.
Conventional optical radiation sensors, by design or orientation, normally sense the output of only one lamp, typically one lamp which is adjacent to the sensor. If it is desirable to sense the radiation output of a number of lamps, it is possible to use an optical radiation sensor for each lamp. A problem with this approach is that the use of multiple sensors introduces uncertainties since there can be no assurance that the sensors are identical in their response. Specifically, vagaries in sensor materials can lead to vagaries in the signals which are sent by the sensors leading to a potential for false information being conveyed to the user of the system.
U.S. Pat. No. 6,512,234 [Sasges et al. (Sasges)] teaches an optical radiation sensor system which allows determination of lamp output information for a single lamp in an array of lamps. An advantage of the Sasges system is that a single sensor device can be moved with respect to the radiation field to allow determination of the dose delivered to the fluid (i.e., in place of the multiple sensors conventionally required as discussed above). More specifically, the optical radiation sensor taught by Sasges allows for on-line determination of ultraviolet (UV) transmittance of the fluid being treated in a UV radiation lamp array.
While optical radiation sensor taught by Sasges is a significant advance in the art, there is room for improvement. Specifically, the field of view of conventional sensor devices (e.g., photodiodes, photoresistors, etc.) is relatively large thereby making it possible for the sensor device to detect in a simultaneous manner the output of more than one lamp. This can be problematic if the object is to determine lamp output information for a single radiation source (e.g., elongate lamp) in an array of radiation sources (e.g., elongate lamps).
One solution to this problem is to restrict the field of view of the sensor device so that the sensor device can “see” only one lamp at any particular point in time. Restricting the field of view of the sensor device to one particular lamp can be accomplished by interposing an appropriately sized circular-shaped aperture between the sensor device and the array of radiation sources (e.g., elongate lamps). As will be described in more detail below, interposition of a circular-shaped attenuating aperture between a sensor device and an array of radiation sources (e.g., elongate lamps) can create a further problem. Specifically, as the particular radiation source (e.g., elongate lamp) and circular-shaped attenuating aperture are moved with respect to one another (typically, the latter will be moved with respect to the former), the area of the lamp “seen” by the sensor device changes. This change in area results in unwanted changes to the radiation intensity detected by the sensor device.
Further, restriction of the field of view of the sensor device so that the sensor device can only “see” one particular radiation source (e.g., elongate lamp) may be accomplished by interposing multiple decreasingly-sized, circular-shaped attenuating apertures between the sensor device and the array of radiation sources (e.g., elongate lamps). The use of such multiple apertures in this manner can result in the intensity of the radiation detected by the sensor device varying sharply as a function of the angular position of the sensor. In the result, any angular (even minor) misalignment of the sensor device with respect to the array of radiation sources will result in an unwanted significant change in detected intensity.
These problems can cause significant errors in detection of radiation intensity from the array of lamps, thereby undermining the reliability of the radiation sensor system.
Accordingly, it would be desirable to have a radiation sensor system which could be used in a dynamic application such as the Sasges sensor system referred to above while obviating or mitigating the detection errors referred to above resulting from the use of a circular-shaped attenuating aperture and/or angular (even minor) misalignment of the sensor device with respect to the array of radiation sources when multiple such circular-shaped attenuating apertures are utilized.